1. Field of the Invention
The present invention relates to a pattern inspection apparatus for inspecting pattern defects on a plate. More particularly, the present invention relates to a pattern inspection apparatus for inspecting defects of a very small pattern in, e.g., a photomask, wafer, or liquid crystal substrate used when fabricating a semiconductor device or liquid crystal display (LCD).
2. Description of the Related Art
The line width/spacing of a pattern constituting a large-scale integrated circuit (LSI) is changing from of the order of submicrons to nanometers, as is represented in 1-gigabit-class dynamic RAMs (DRAMs). One of the major factors that decrease the yield of the manufacture of LSIs is pattern defects in a photomask. The photomask is used when exposing and transferring an ultra-small pattern onto a semiconductor wafer by photolithography. In particular, as the pattern size of LSIs formed on semiconductor wafers shrinks, the size that must be detected as a pattern defect shrinks considerably. Hence, an apparatus that inspects such defects is under active development.
As the multimedia-oriented society progresses, the liquid crystal substrate size of LCDs is increasing toward 500 mm×600 mm or more. Also, the pattern of a TFT or the like to be formed on the liquid crystal substrate is shrinking. Accordingly, inspecting a very small pattern defect over a wide range is required. For this purpose, development of a pattern inspection apparatus that inspects a pattern defect in a photomask used when manufacturing a large-area LCD pattern and a large-area LCD within a short period of time efficiently is urgently needed.
Regarding a conventional photomask defect inspection apparatus, a die-to-database inspection scheme and a die-to-die inspection scheme are known (for example, see Jpn. Pat. Appln. KOKAI Publication No. 2002-139450). According to the die-to-database inspection scheme, a pattern on the mask is detected with inspection optics. Reference pattern data is obtained from design pattern data used in the fabrication of the mask. The detected pattern data and the reference pattern data are compared in accordance with an appropriate algorithm. The die-to-die inspection scheme is based on the premise that the photomask has a plurality of areas having the same patterns. Detected pattern data of the areas are compared to each other.
Usually, when die-to-die inspection is to be performed, the operator must specify in advance which dies are to be inspected from data acquired with optics. These optics can scan the pattern image of an inspection target object with a magnification of 1× to not more than about 100×. The operator must also instruct the origin coordinates, size, and the like of the die. This operation requires much labor and skill, leading to a decrease in inspection throughput.
Therefore, a pattern inspection apparatus that can perform die-to-die comparative inspection if the operator does not specify which dies are to be inspected, thus improving the inspection throughput, has been sought.